The present invention pertains to antenna systems, including more particularly to antennas with directionally selectable transmission capabilities.
In wireless voice and data applications, both wireless local loop (WLL) and mobile applications, system capacity remains an important design issue since the power available to a wireless device is often limited. Interference with other devices also limits the system capacity. When operating from a battery supply, such as with a wireless phone, pager, or modem, this problem is exacerbated.
In mobile wireless applications, such as cell phones, pagers, and wireless modems, the spatial orientation of the device antenna is not static (i.e. the user is often moving, or the device itself is moving). Since the instantaneous orientation of the antenna is essentially unknown to a designer of these devices, known wireless systems have addressed this design problem by providing an omni-directional antenna. Omni-directional antennas produce a substantially constant radiation pattern in essentially all directions in at least one plane. While this effectively ensures that the antenna signal reaches an intended base station regardless of the orientation of the antenna or wireless device, it does so at the cost of wasted power and the potential for interference with other users and electronic systems. Whip antennas (long, thin extending antennas) that are often incorporated into cellular phones and other wireless voice and data systems, often utilize this omni-directional transmission technique. This will be the case regardless of where the base station is positioned in relation to the wireless device.
Several problems still remain with the use of these known omni-directional antennas and the use of an omni-directional transmission scheme. First, since an omni-directional antenna radiates in all directions at all times, the transmission may interfere with the other non-target base stations that are within the transmission range of the antenna. As a result, these systems may impact the overall system capacity. Second, since for a given coverage distance, omni-directional antennas have a lower gain than a similarly powered antenna that has a more focused directivity, a larger transmitter power is typically required to effectively operate them. Increasing the transmitter power usually results in increased heat, increased product cost, and increased power consumption, all of which are undesirable.
Known Radio Frequency switching devices that can selectively couple a signal with a particular output, often employ a capacitive junction that functions as a switch to turn the device on or off. In systems that demand complete isolation from the remainder of the circuit, the use of these devices still may present problems due to the remaining capacitance in the off-state. This may limit their ability to provide complete isolation. Since it is still desirable to use these devices due to their low cost and wide availability, a system that cancels the effect of this capacitance is needed.
The present invention comprises an antenna with selectably activated radiating elements. In a first embodiment, an antenna comprises a dielectric body and a radiating element formed on the dielectric body. The antenna also comprises a transmission line and a switching device, the switching device has an input and an output, the input is connected to the transmission line and the output is connected to the radiating element.
In another embodiment, an antenna having an exterior surface comprises a plurality of radiating elements formed on the exterior surface of the antenna and switching circuitry connected to said plurality of radiating elements and said transmission line.
In another embodiment, an antenna comprises a dielectric body having an interior and an exterior surface. A plurality of radiating elements is formed on the exterior surface of the antenna body. The antenna also comprises a transmission line and a switching device operative to selectively connect the transmission line with at least one of the radiating elements.
Other embodiments will become apparent hereinafter.